Cyclones are used in the main for separating a liquid phase from a gas/vapour phase. In industry today, use is in general made of cyclones which are specially manufactured with regard to the operating conditions in which the cyclone is principally to work. This trend towards special manufacturing leads to a small batch size, which in turn gives rise to relatively high costs. Furthermore, cyclones known today are in most cases constructed in such a manner that they cannot be adapted to different operating conditions, at least not without a considerable effort, as a result of which they often, in the event of a change in the production process, come to be used in operating conditions which are not optimum.
GB-A-550260 and U.S. Pat. No. 3,516,551, for example, show that this last-mentioned problem has been known for a long time and that there is a number of proposals for solutions of said problem. Common to known solutions, however, is the fact that flow variations are compensated in direct connection with the inlet into the cyclone by, in the case of a small flow, reducing the flowthrough area in the inlet arrangement of the cyclone so that the inlet rate is kept almost constant in order to obtain an optimum separation and by, in the case of a large flow, doing the opposite. In the case of liquids with a tendency to foam, however, such a solution proves to have undesirable after-effects, since the regulation gives rise to a change in the flow pattern and causes a pressure drop which in turn, because of the vapour formation etc., leads to an uneven flow pattern in connection with the outflow inside the cyclone and is thus a cause of foam formation. Foam formation is very disadvantageous since it disturbs the flow conditions inside the cyclone and thus counteracts optimum operating conditions.